[Suzu]

A clearer version of what ZeoRangerV said for those who don't know about the terms:

Showa era (when Japan's emperor was Hirohito): December 25th 1925 to January 7th 1989 -> Includes Goranger to Liveman (12)

Heisei Era: January 8th 1989 till today and as long as Akihito is still Japan's emperor -> Includes Turboranger to Toqger and onwards (26)

We didn't have long breaks in Sentai as we had with Kamen Rider, so the number of Heisei teams is far too large to make a Showa vs. Heisei movie or special of some sort- at least not if it's supposed to be fair.

So we could have, say, Goranger to Liveman vs. Turboranger to Timeranger, but that would leave out all the newer Teams.